Front end and high frequency receiver having quadrature low noise amplifier

ABSTRACT

A front end and a high frequency receiver ( 1 ) provided therewith are described, which front end comprises a quadrature low noise amplifier ( 2 - 1, 2 - 2 ) as a low noise amplifier. A high isolation between local oscillators ( 6 - 1, 6 - 2 ) and quadrature mixers ( 3 - 1, 3 - 2 ) is achieved thereby, reducing a DC offset at mixer outputs ( 7, 8 ). The quadrature low noise amplifier may be implemented as a differential class AB cascade arrangement of MOST or FET semiconductors ( 15 ). A low distortion receiver ( 1 ) having a high linearity is the result.

The present invention relates to a front end for a high frequencyreceiver, which front end comprises a low noise amplifier.

The present invention also relates to a high frequency receiver, whichis provided with such a front end comprising a low noise amplifier, andwhich is provided with quadrature mixers coupled to the low noiseamplifier, and relates to a quadrature low noise amplifier forapplication in the high frequency receiver.

The present invention also relates to a communication device, forexample a radio receiver, transceiver or a telephone, such as a mobileor cordless telephone provided with such a high frequency receiver.

Such a receiver is known from the article ‘A 1.9-GHz Wide-Band IF DoubleConversion CMOS Receiver for Cordless Telephone Applications’, By J. C.Rudell et al, IEEE Journal of Solid-State Circuits, vol. 32, No. 12,December 1997, pages 2071-2088. Several possible receiver architecturesare disclosed in the article, wherein the high radio frequency (RF)front end of the receiver successively comprises an antenna, an RFfilter, a low noise amplifier followed by intermediate frequency (IF)and mixer stages. One or more local oscillators (LO) are used for mixingan RF signal to the IF frequency, which may also be a near zero, or zerofrequency signal. The problem of local oscillator signal leakage tomixer inputs, moderate LO isolation and self-mixing is known to resultin unwanted even varying DC offsets at outputs of the various mixers.The DC offsets in turn give rise to reduction of the dynamic range ofthe receiver requiring additional technical measures, which aredifficult to integrate on a limited chip area, increase costs, as wellas power consumption.

Therefore it is an object of the present invention to provide an RFfront end and RF receiver, which may be integrated fully on a limitedchip area against reduced costs, and which gives rise to reduced DCoffsets.

Thereto the front end and high frequency receiver according to theinvention are characterised in that the low noise amplifier (LNA)circuit is a quadrature LNA circuit.

It is an advantage of the front end and HF receiver according to thepresent invention that the inventor has realised that by introducing aquadrature LNA circuit in front of the quadrature mixers, inputs of themixers are being isolated by the quadrature LNAs. As a consequenceleakage of the quadrature local oscillator signals to the mixer inputsis effectively prevented, which reduces DC offsets at outputs of themixers. In addition this reduction increases the dynamic range of thehigh frequency receiver according to the invention. Furthermore it hasbeen found that the quadrature LNAs may even for certain applicationshave a moderate amplification factor around one, or lower, such thatsimple quadrature impedance transformers result. This reduces the powerconsumption of these LNA transformers and decreases their occupied ICchip area.

An embodiment of the high frequency receiver according to the inventionis characterised in that quadrature paths of the quadrature low noiseamplifier are implemented differentially. This advantageously results inreduced second order distortion effects. In addition sensitivity towardssubstrate bouncing is decreased, which means that again signaldistortion is kept to a minimum.

A further embodiment of the high frequency receiver according to theinvention is characterised in that the differential quadrature low noiseamplifier is constructed as a class AB operating circuit.

Such an embodiment has a high linearity, which reduces intermodulationdistortion, but is also capable of providing sufficient output currentfor driving further circuitry which is coupled to such a class ABoperating circuit.

A still further embodiment, which is easy to implement and has a reducednumber of components to realise the high frequency receiver according tothe invention is characterised in that the quadrature low noiseamplifier comprises a cascode arrangement of semiconductors.

Suitable preferred semiconductors are of the type MOST, such as NMOST orPMOST, or FET, such as MESFET, or the like.

Another embodiment of the high frequency receiver according to theinvention is characterised in that across the cascode arrangement ofsemiconductors there is connected a capacitor.

Advantageously this capacitor acts as a local battery for the cascodearrangement of semiconductors, and also serves to decrease thirdharmonic distortion by approximately 10 dB.

An embodiment of the high frequency receiver according to the invention,which is preferred because it improves linearity by cancelling gainmismatch between the quadrature LNAs, is characterised in that the highfrequency receiver comprises two quadrature choppers coupled betweenrespective outputs of the quadrature low noise amplifiers and respectiveinputs of the quadrature mixers.

If in still another embodiment of the high frequency receiver accordingto the invention the receiver is characterised in that the quadraturechoppers and quadrature mixers are combined to passive quadraturechoppers/mixers, then a still further decrease of power consumption canbe realised, which is also very important in relation to developmentstowards a one chip receiver.

Similar advantages and favourable results can be mentioned for acommunication device, for example a radio receiver, transceiver or atelephone, such as a mobile or cordless telephone provided with such ahigh frequency receiver.

At present the high frequency receiver according to the invention willbe elucidated further together with its additional advantages whilereference is being made to the appended drawing, wherein similarcomponents are being referred to by means of the same referencenumerals. In the drawing:

FIG. 1 shows a simplified block diagram of a high frequency receiveraccording to the present invention;

FIG. 2 shows a possible embodiment of a passive quadrature chopper forapplication in the high frequency receiver of FIG. 1; and

FIG. 3 shows a passive embodiment of a differential cascode arrangementof semiconductors implementing the one of the quadrature low noiseamplifiers.

FIG. 1 shows a block diagram of a high frequency receiver 1, inparticular its so called front end. In the front end such a receiver 1comprises an low noise amplifier 2 in the form of quadrature low noiseamplifiers 2-1 and 2-2, hereafter LNAs 2, which are coupled through aterminal indicated ‘input’, and usually a band-pass filter and/orantenna switch (both not shown) to an antenna (also not shown). Thereceiver 1 also comprises an I-mixer 3-1 and a Q-mixer 3-2, which may inone embodiment be coupled directly to outputs 4 and 5 of the I and QLNAs 2-1 and 2-2 respectively. The quadrature mixers 3 are coupled toquadrature outputs I_(o) and Q_(o) of generally one local oscillator 6,and mixer IF outputs 7 and 8 are coupled to a quadrature demodulator(Demod) 9, which may for example include a sigma-delta demodulator orany other suitable demodulator. Such a receiver scheme having an I and aQ path as indicated can be used in for example a—possibly multistage—IFreceiver, such as a zero IF, near zero IF receiver or the like. Inparticular in a communication device such as a radio receiver,transceiver or a telephone, for example a mobile or cordless telephoneprovided with such a high frequency receiver 1. By including thequadrature LNAs 2 in the receiver 1 the local oscillator output signalsI_(o) and Q_(o) from the oscillator 6 are prevented from cross mixing orself mixing, such that DC offsets occur at differential mixer outputs 7and 8. This leads to a receiver 1 having an improved dynamic range.

The receiver 1 may in a further embodiment comprise quadrature choppers10-1 and 10-2. FIG. 2 shows an embodiment of a possibly passivequadrature chopper 10 for application in the high frequency receiver 1.The chopper 10 switches I and Q signals in quadrature paths I and Q ofthe receiver 1 to improve linearity by cancelling a possible gainmismatch between the LNAs 2-1 and 2-2. The embodiment of the chopper 10is preferred in that it is a combined chopper mixer structure, which inaddition is passive, as a result of which it shows a reduced powerconsumption. The passive chopper mixer 10 has a structure which is easyto implement on a chip with only a very moderate chip area. It consistsof parallel coupled semiconductors 11-1, 11-2 and cross coupledsemiconductors 12-1, 12-2 connecting differential inputs 13 and 14. Thesemiconductors 11 and 12 if properly controlled and timed on theirrespective gates by local oscillator signals LO or their inverse LO withupper score, achieve a simultaneous mixing and chopper action by thesame kind of passive low power consuming structure.

A from a viewpoint of high linearity and high isolation preferredembodiment of an I or Q LNA 2 is shown in FIG. 3. It shows a passive lowpower consuming differential cascode arrangement of semiconductors 15-1. . . 15-8 implementing such a quadrature low noise amplifier. Input 16,which is a differential input in this case is coupled to two branches,each having four semiconductors 15. Also output 17, which corresponds toearlier inputs 4 and 5, is a differential output in this case and thisoutput 17 is isolated from the input controlled semiconductors 15-1,15-4, 15-5, 15-8 by isolating semiconductors 15-2, 15-3, 15-6, 15-7respectively. This results in a high isolation value between input 16and output 17, which is now very well isolated from the input 16, inorder to reduce self mixing by the local oscillator signal that may bepresent at the output 17, which is coupled to the mixer 3 or the chopper10.

The LNA 2 of FIG. 3, apart from circuit impedances Z1 and is coupled tosupply voltage Vdd and earth respectively, further has a capacitor Ccoupled as shown across the cascaded semiconductors 15. This capacitor Cacts as a battery or voltage source to the cascode arrangement, reducesthird order distortion of the LNA and provides an improved linearity tothe arrangement. The arrangement of semiconductors 15 is a class ABcircuit, so that an effective output current may be provided by thedifferential output 17 to further circuitry coupled therewith. Generallythe semiconductors 15 are of the type MOST, such as a NMOST or a PMOST,or of the type FET, such as a MESFET, or the like.

Whilst the above has been described with reference to essentiallypreferred embodiments and best possible modes it will be understood thatthese embodiments are by no means to be construed as limiting examplesof the devices concerned, because various modifications, features andcombination of features falling within the scope of the appended claimsare now within reach of the skilled person.

1.-11. (canceled)
 12. A high frequency receiver that is provided with afront end comprising: first and second quadrature mixers; first andsecond quadrature choppers respectively coupled between respectiveinputs of the respective ones of the first and second quadrature mixers,the choppers configured to switch in-phase and quadrature signalsrespectively.
 13. The high frequency receiver according to claim 12,wherein quadrature paths of the first and second quadrature choppers areimplemented differentially.
 14. The high frequency receiver according toclaim 13, wherein respective inputs of the first and second quadraturechoppers are coupled to differential first and second quadrature lownoise amplifiers and wherein the differential first and secondquadrature low noise amplifiers are constructed as a class AB operatingcircuits.
 15. The high frequency receiver according to claim 13, whereinthe first and second quadrature choppers are configured to cancel a gainmismatch between the first and second quadrature low noise amplifiers.16. The high frequency receiver according to claim 12, wherein theoutputs of the first and second mixers are coupled to a quadraturedemodulator configured to demodulate signals output from the first andsecond mixers respectively.
 17. The high frequency receiver according toclaim 12, wherein the quadrature choppers and quadrature mixers arecombined into passive quadrature choppers/mixers.
 18. The high frequencyreceiver according to claim 17, wherein the passive quadraturechoppers/mixers comprises parallel coupled semiconductors and crosscoupled semiconductors.
 19. The high frequency receiver according toclaim 12, wherein the first and second quadrature mixers are included ina receive circuit of said receiver, and wherein output of said first andsecond mixers comprises a signal that has been down-converted by saidreceive circuit
 20. The high frequency receiver according to claim 12,further comprising a local oscillator coupled between the first andsecond mixers, the local oscillator configured to provide controlsignals to each of the first and second mixers respectively.
 21. Thehigh frequency receiver according to claim 12, wherein each of saidchoppers switches its respective outputs for coupling with the outputsof the other of said choppers.
 22. A passive quadrature chopper/mixerfor use in a high frequency receiver, the passive quadraturechopper/mixer comprising: first and second quadrature mixers; first andsecond quadrature choppers respectively coupled between respectiveinputs of the respective ones of the first and second quadrature mixers,the choppers configured to switch in-phase and quadrature signalsrespectively.
 23. The passive quadrature chopper/mixer according toclaim 22, wherein quadrature paths of the first and second quadraturechoppers are implemented differentially.
 24. The passive quadraturechopper/mixer according to claim 23, wherein respective inputs of thefirst and second quadrature choppers are coupled to differential firstand second quadrature low noise amplifiers and wherein the differentialfirst and second quadrature low noise amplifiers are constructed as aclass AB operating circuits.
 25. The passive quadrature chopper/mixeraccording to claim 23, wherein the first and second quadrature choppersare configured to cancel a gain mismatch between the first and secondquadrature low noise amplifiers.
 26. The passive quadraturechopper/mixer according to claim 22, wherein the outputs of the firstand second mixers are coupled to a quadrature demodulator configured todemodulate signals output from the first and second mixers respectively.27. The passive quadrature chopper/mixer according to claim 22, whereinthe passive quadrature choppers/mixers comprises parallel coupledsemiconductors and cross coupled semiconductors.
 28. The passivequadrature chopper/mixer according to claim 22, wherein the passivequadrature chopper/mixer is included in a receive circuit of saidreceiver and wherein output of said first and second mixers comprises asignal that has been down-converted by said receive circuit.
 29. Thepassive quadrature chopper/mixer according to claim 22, furthercomprising a local oscillator coupled between the first and secondmixers, the local oscillator configured to provide control signals toeach of the first and second mixers respectively.
 30. The passivequadrature chopper/mixer according to claim 22, wherein each of saidchoppers switches its respective outputs for coupling with the outputsof the other of said choppers.
 31. A high frequency receiver which isprovided with a front end comprising: first and second quadrature mixersadapted to coupled to respective ones of a first and second low noiseamplifier; first and second quadrature choppers adapted to respectivelycoupled between respective outputs of the respective ones of the firstand second quadrature low noise amplifier, and respective inputs ofrespective ones of the first and second quadrature mixers, the outputsof the first and second mixers being demodulated by a quadraturedemodulator, wherein each of said choppers switches its respectiveoutputs for coupling with the outputs of the other of said choppers.